Current dinner boxes like lunch box, picnic box, snack box, etc. typically consist of cap and body. Food is placed in the box body, which features convenience of carrying and ease of use. To prevent outflow and leak of food liquor in the process of carrying, some dinner boxes are provided with sealing devices, e.g. Patent 86210848, 87216769, 89200752, 94222756, etc. Their sealing devices are made up of locking mechanism like clamp and screw, and sealing components, whose designs feature such disadvantages as complicated structure and high cost, and are not applicable to cheap plastic or paper snack boxes. Patent 89218416 is a kind of plastic snack box that employs two concave-convex benched self-locking devices instead of original plane anastomosis. It cannot be opened by itself but with outside force, and also improves sealing performances. However, it may deform under pressing and squeezing; thus a clearance may appear in the clamping part between the cover and the body, which cannot effectively prevent the outflow of food liquor.